The invention relates to a sloping-edge-controlled injection pump for internal combustion engines. Such a pump is usable as a direct injector for commercial vehicles and the like. Injection pumps of this kind have been contemplated which comprise two feed bores, lying at the same level and diametrically opposite, in the pump cylinder, in which a cam-operated pump plunger, defining the pump working chamber and having an upper control edge effecting the start of delivery and a lower sloping control edge effecting the end of delivery, is guided axially and in a rotationally movable manner, and furthermore grooves are provided for effecting the interruption in delivery, including a peripheral groove in the pump plunger and a by-pass groove in the pump cylinder.
It is known that activities worldwide are directed towards reducing the emissions from commercial vehicles. Increasing demands with regard to greater efficiency and low pollution as well as noise thresholds must be met. To considerably reduce the combustion noises, preinjection systems in particular are suitable in order to control the release of heat in the compression-ignition engine in such a way that a combustion-chamber pressure pattern favorable with regard to the stimulation of noise develops. Complicated combustion processes with two injection pumps and two separate injection nozzles have been discontinued in view of the immense costs.
GB Patent Specification 893, 621 discloses simplified embodiments of sloping-edge-controlled fuel injection pumps which, through a certain groove and hole geometry in the pump cylinder and in the pump plunger, split up the injection into preinjection and main injection with a timed interruption in between. Due to the bores, arranged vertically offset, in the pump cylinder and due to the sloping-edge-control on one side, all the embodiments produce nonuniform flow loading of the pump plunger, which certainly occurs to a smaller extent in the embodiment according to FIG. 5 on account of the feed bores lying at the same level, but the groove geometry here leads to relatively large preinjections (size of stroke x), resulting in inadequate noise reduction.
Compared with the embodiment having preinjection and main injection disclosed by GB Patent Specification 893,621, an object of the invention, apart from a further improvement with regard to noise reduction, is also to enable more uniform loading of the pump plunger performing the stroke.
According to the invention, this object is achieved by providing a pump of the above noted type, wherein a further bypass is made in the pump cylinder and a further peripheral groove is made in the pump plunger in such a way that the two respective bypasses and peripheral grooves, as well as two stop grooves provided between the peripheral grooves and extending from the upper to the lower control edge are arranged in a rotationally symmetric manner, and wherein each bypass partly overlaps the feed bores in the projection perpendicular to the axis of the pump cylinder.
Non-uniform flow loading of the pump plunger and, as the worst consequence thereof, breakdown of the lubricating film between pump cylinder and plunger as well as the risk of a tendency to seize are avoided by the special measures according to preferred embodiments of the invention, namely to provide a rotationally symmetric groove geometry. In addition, due to the overlap (feed bores/bypasses) in the double-flow system, a relatively small preinjection quantity is obtained which has a favorable effect on the injection-quantity variation oriented to requirements and therefore on a particularly favorable noise reduction.
U.S. Pat. No. 4,445,828 discloses a fuel injection pump in which two feed bores are arranged in the pump cylinder and upper control edges and also two sloping grooves are arranged on the pump plunger for controlling the delivery, which certainly enable uniform flow loading of the pump plunger and also produce advantages relating to combustion through the increase in the flow cross-sections which results from the double-flow capacity but have an adverse effect on the combustion noises on account of the cross-sectional increase. In the embodiment according to the invention, having measures relating to control, this disadvantage does not occur during any injection operation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.